A friend of mine has a 1999 Chevy Astro which refused to start one day, a week after I replaced a badly leaking CMPI unit (spider) on it. I performed a fuel pressure test and found that, as long as the pump was running, it was getting 65 psi (spec is 60-66), but the pressure would bleed off once the pump had shut off. I switched the key off and on several times, and the pressure finally stopped bleeding off, and the engine started. When running, the needle on the fuel pressure gauge flutters rapidly between 52 and 54 psi, which I’m not sure is normal or not. I have heard there is a valve or regulator of some kind in the sending unit that causes this pressure bleed-off problem and its associated no-start condition, and that this valve is not serviceable; the pump/sending unit must be replaced. Is this true? These folks say this will be the fifth sending unit they have had in this van, and if I can save them some money by not replacing this whole $300 sending unit that would be great since money’s tight for them right now.
The fuel pressure should read 60-65 PSI with the engine running. If the fuel pressure is below specs and is fluctuating, plus the fact that the fuel pressure bled off rapidly points to a worn fuel pump.
Thanks, Tester. I thought there was a different spec for running fuel pressure than static pressure, but could find nothing. I also just wanted to make absolutely certain replacing the fuel pump was the only solution before telling them to spend that much money. Again. It’s unfortunate these things are such junk.
I assume you replaced the CPI unit with an updated one that replaces the poppet nozzles with actual injectors. Did you also replace the line kit that runs from the rear of the intake to the CPI unit? I’ve seen those develop hairline cracks. I’d pull the upper intake and pressureize the fuel system to be sure there are no internal leaks.
The new one is the new style, as was the one I removed. The engine runs great now (when it will start), whereas before replacing the injector unit it ran very rich, belched black smoke and misfired a lot. I did not replace the line set because I did not see anything wrong with it. There is no evidence of a fuel leak at the line set or anywhere else, no fuel odor or anything since replacing the leaking injector unit. Once I got the van to start, I drove it from their house to mine (about 7 miles). I allowed it to sit for a couple hours with the fuel pressure gauge on it, and it lost 2 psi in those two hours and restarted when I tried it, although it cranked a little longer than it should have (maybe three seconds).
Hmm. 2 psi loss in two hours is nothing. I think you’re going to have to verify a low fuel pressure condition during a no start to condemn the fuel pump module. Even if the pressrue bleeds off quickly due to a failed check valve in the pump, if the pump can generate the required 60psi within 2 seconds of cranking the engine should still start.
Were you able to determine where the old unit was leaking?
BTW, the newer style injectors will tolerate a lower fuel pressure on start-up than the old poppet nozzles. They simply would not open at less than 60psi.
I did not verify where the previous injector unit was leaking, I just pulled the plenum and found everything covered in damp carbon and soot that smelled like gasoline. As I stated in my original post, upon hooking up the test gauge, the pressure would quickly bleed off as soon as the pump quit running. The engine would not start and pressure would dip to around 30 psi or so. After that, I kept turning the key off and on to see if I could get the pressure to build and stay consistent. Eventually, it did, which is when I tried starting the engine and it fired up. I have heard that this usually means the check valve is bad and was mostly wondering if there is a way to correct the check valve problem without replacing the entire pump/sending unit.
Yeah, it sounds like a fuel pump problem if you’re sure there are no leaks anywhere. That pump module is only serviced as a unit though, the only replaceable part is the gauge sender, but you’ve got to pull the tank and remove the module to do anything. When you pull the tank be sure the wiring harness that plugs into the module shows no signs of overheating or poor connection. If the pump has been replaced before the harness better have been too.
That’s what I thought. I just wanted to make sure there wasn’t a cheaper way to get their van back on the road before having them purchase a whole new pump module. Thanks for your help.